This invention generally relates to an improved process for preparing squaraine compositions, and more specifically, the present invention is directed to an improved process for the preparation of mixed squaraine compositions of matter. In one embodiment, the present invention involves the preparation of certain mixed compositions by the reaction of a dialkyl squarate with dialkylaniline derivatives, and dialkylhaloanilines. The mixed squaraine compositions resulting from this process are useful for incorporation into layered photoresponsive imaging devices wherein, for example, the sensitivity thereof can be varied or enhanced, enabling these devices to be capable of being responsive to visible light, and infrared illumination needed for laser printing, where for example gallium arsenide diode lasers are selected. Accordingly, there is envisioned photoresponsive imaging members containing the mixed squaraine compositions prepared in accordance with the process of the present invention, situated between a photogenerating layer and a hole transport layer, or situated between a photogenerating layer and a supporting substrate of the member. The mixed squaraine compositions prepared in accordance with the process of the present invention also possess high charge acceptance, and low dark decay values, as well as excellent photosensitivity.
Layered photoresponsive imaging members with photogenerating layers and transport layers are known, reference U.S. Pat. No. 4,265,990. Examples of photogenerating layers disclosed in this patent include trigonal selenium, and phthalocyanines, while examples of transport layers that may be selected are comprised of certain diamine dispersed in an inactive resinous binder composition. Photoconductive imaging members with certain squaraine compositions, particularly hydroxy squaraines, are also known. There is thus disclosed in U.S. Pat. No. 4,415,639 the use of certain squaraine pigments, inclusive of hydroxy squaraines, in photoresponsive imaging devices. Specifically, there is described in this patent, the disclosure of which is totally incorporated herein by reference, an improved photoresponsive device comprised of a substrate, a hole blocking layer, an optional adhesive interface layer, an inorganic photogenerating layer, a hydroxy squaraine photoconductive composition capable of enhancing or reducing the intrinsic properties of the photogenerating layer, and a hole transport layer. Additionally, there is disclosed in U.S. Pat. No. 3,824,099 certain photosensitive hydroxy squaraine compositions. According to the disclosure of this patent, the squaraine compositions are photosensitive in normal electrostatographic imaging systems.
Additionally, in U.S. Pat. No. 4,471,041, there is illustrated squaraine compositions of matter, such as bis-9-(8-hydroxyjulolidinyl)squaraine, and the use of these compositions as imaging members. One of the imaging members disclosed is comprised of a supporting substrate, a hole blocking layer, an optional adhesive interface layer, an inorganic photogenerating layer, and a squaraine photoconducting composition layer capable of enhancing or reducing the intrinsic properties of the photogenerating layer.
Processes for preparing squaraine compositions generally involve the reaction of squaric acid with an amine. Thus, for example, the novel julolidinyl squaraine compositions disclosed in the referenced U.S. Pat. No. 4,471,041 patent are prepared by the reaction of an aromatic amine and squaric acid, in a molar ratio of from about 1.5:1 to 3:1, in the presence of a mixture of an aliphatic alcohol and an optional azeotropic cosolvent. About 200 milliliters of alcohol per 0.1 mole of squaric acid are used, while from about 40 milliliters to about 4,000 milliliters of azeotropic material are selected. The squaric acid reaction is generally accomplished at a temperature of from about 50 degrees Centigrade to about 130 degrees Centigrade. Illustrative examples of amine reactants include 8-hydroxyjulolidinyl, while examples of aliphatic alcohol selected include 1-butanol, with the azeotropic materials being aromatic compositions such as benzene and toluene. Moreover, there is disclosed in a copending application, U.S. Ser. No. 557,796/83, now U.S. Pat. No. 4,525,592, entitled Synthesis of Photoconductive Squaraines, the disclosure of which is totally incorporated herein by reference, processes for preparing squaraine compositions by the reaction of a dialkyl squarate and an aromtic aniline. More specifically, there is disclosed in this copending application an improved process for the preparation of squaraine compositions which comprises reacting a dialkyl squarate with an aniline in the presence of an acid cataylst and an aliphatic alcohol, at a temperature of from about 60 degrees Centigrade to about 160 degrees Centigrade.
There is also disclosed in a copending application U.S. Ser. No. 570,563, now U.S. Pat. No. 4,524,218, entitled Process For The Preparation Of Squaraine Compositions, the disclosure of which is totally incorporated herein by reference, a process for the preparation of photoconductive squaraines wherein the known squaric acid reaction is accomplished in the presence of a phenol, or a phenol squaraine. Further, there is disclosed in copending application U.S. Ser. No. 557,795, now U.S. Pat. No. 4,521,621, the disclosure of which is totally incorporated herein by reference, a process for obtaining novel unsymmetrical squaraine compositions from squaric acid, wherein there is formed a mixture of squaric acid, a primary alcohol, a first tertiary amine, and a second tertiary amine.
In another copending application, U.S. Ser. No. 06,038/84, entitled Processes For The Preparation Of Mixed Squaraine Compositions, there is described the reaction of squaric acid, an aromatic amine, and a fluoroaniline. The disclosure of this copending application is totally incorporated herein by reference.
While the above processes for preparing squaraine compositions may be suitable for their intended purposes, there continues to be a need for other processes wherein mixed squaraine compositions, useful as photoconductive materials, can be prepared. Additionally, there remains a need for simple, economical processes for preparing mixed squaraine compositions wherein the squaraine products obtained contain substantially less impurities than those squaraines resulting from the squaric acid process, as it is believed that the presence of impurities in the squaraine compositions resulting from the squaric acid process causes the photosensitivity of these compositions to vary significantly, and in many instances, to be lower than the squaraine compositions prepared in accordance with the process of the present invention. Further, there continues to be a need for mixed squaraine compositions which, when selected for layered photoresponsive imaging devices, allow the generation of acceptable images, and wherein such devices can be repeatedly used in a number of imaging cycles without deterioration thereof from the machine environment or surrounding conditions. Moreover, there remains a need for processes for preparing certain mixed squaraine compositions, wherein the resulting products when incorporated into imaging members exhibit excellent dark decay and superior photosensitivity. Also, there is provided in accordance with the process of the present invention xerographic photoconductive imaging members comprised of mixed squaraine photogenerating materials possessing desirable sensitivity, low dark decay, high charge acceptance values, and desirable dispersion particle sizes.